Cats with recessively inherited mucopolysaccharidosis VI (Maroteaux-Lamy Syndrome) will be mated and the pre-natal and post-natal ontogeny of the ocular lesions studied by light and electron microscopy. Emphasis will be placed on the pigment epithelial hypertrophy that occurs in affected animals. The relation of phagocytosis of rod outer segments to the development of intracytoplasmic vacuolated inclusions will be investigated. The influence of outer segment renewal rates, light exposure, pigmentation and enzyme replacement therapy in the temporal and spatial distribution of disease within the retinal pigment epithelium will be investigated.